JPS61204316A - Local softening device for link chain - Google Patents

Abstract

PURPOSE:To improve working efficiency and to make possible mass production by constituting the titled device in such a manner that only the part requiring a heat treatment can be limited and be locally softened and that the heat treat ment temp. can be easily and exactly set and held. CONSTITUTION:A link chain 11 is arrayed to one strength length and is continuously conveyed by guide rails 22 and a link feed mechanism 25. After the scale sticking thereto is removed by wire brushes 26, respective links 5 are held by each piece in a horizontal state by means of link positioning levers 27of a heater 28. The held links 5 are grasped from above and below by electrodes 29 and thereafter electricity is conducted between both upper and lower electrodes 29 through the links 5 to harden the local part clamped between the electrodes 29 by the Joule heat. The heated part of the link 5 is cooled and tempered by the cooling water injected from nozzles 31.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] When manufacturing link chains used in chain blocks, fishing net chains, etc., the present invention automatically heat-treats the entire link and then locally heat-treats the link. This invention relates to a link chain local softening device that can perform softening treatment.

[Technical Background of the Invention] Generally used manual chain hoists, electric chain hoists, fishing net chains, and sling chains are
It uses a link chain made by chaining together many links.

The link chain has a parallel section 1.2 as shown in FIG.
A large number of oval annular links 5 having arcuate shoulders 3 and 4 are fitted and connected to each other, and each link 5 is welded at its joint end 6 on its parallel portion 1 or 2. ing. Now, when a load is applied to the link 5, the shoulder portion 3,
4, while tensile force F acts in the vertical direction (outside),
As a result of the bending force F' acting inwardly on each parallel portion 1.2, the stress distribution becomes as shown by the dotted line in FIG.

Therefore, the link 5 is required to have a sufficient breaking elongation as well as hardness to withstand breaking load and Charpy resistance, so generally, the entire link 5 is heat-treated at a predetermined temperature in the next process after the above-mentioned chain, processing or welding is completed. (quenching and tempering) to obtain a sufficient tempered martensitic structure.

However, as described above, since this link 5 is partially welded, the welded portion has the following drawbacks.

(1) In the welded part, a metallic structure change occurs in the base metal due to high-temperature local heating, and the crystal grains become coarse and become close to a so-called cast structure, resulting in extremely poor toughness.

(2) Residual stress is generated in the welded part due to rapid cooling, rapid heating, and heating.

(3) On the inside of the weld, surface defects that cause notch effects are likely to occur due to the flow of molten steel.

Because of these problems, when a large load is applied, the load is most concentrated at the welded part.

Therefore, even if only the entire link 5 is quenched and tempered to a predetermined hardness, the welded portion is fragile and accidents often occur in which the link 5 breaks.

Conventionally, as a countermeasure for this, re-quenching and tempering was performed only on the parallel portion 1.2 to partially soften the hardness, and usually multiple expensive high frequency induction heating furnaces were installed in parallel. On the other hand, after the entire Link 5 was heat-treated, the other machine was partially heat-treated.

However, the magnetic field formed by the high-frequency induction coil does not have a clear area, so it really needs to be softened.

That is, as a result of induced currents occurring in areas other than the welded area, a fairly wide area was heat treated and localized softening treatment was impossible.

In addition, in the case of high-frequency induction heating, the frequency must be made higher to increase the induced current and Joule heat, but conversely, the quenching and tempering treatment layer becomes thinner due to the skin effect, so Coupled with the expansion of the area, it has been difficult to set the heat treatment temperature and maintain an accurate quenching temperature.

Of course, in addition to the high-frequency electric furnace, gas burners have also been used, in other words, placing a torch at a predetermined part of the link 5 to heat the link 5 locally, but this is inefficient and does not allow accurate temperature control. It is rarely practiced today because it is difficult and post-processing is troublesome.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and does not use an expensive high-frequency induction heating furnace for local softening treatment of links.
It is possible to locally soften only the parts that truly require heat treatment, and the heat treatment temperature can be easily and accurately set and maintained.It is also excellent in terms of work efficiency and quality control, and is suitable for mass production. The purpose of this invention is to provide a chain local softening device.

[Summary of the Invention] In order to achieve the above object, a link chain local softening treatment apparatus according to the present invention includes a guide rail for guiding a link chain that has been entirely heat treated in a heating furnace, and a link chain that has been transferred to a predetermined position. The link chain is comprised of a link positioning mechanism that positions the link, a plurality of electrodes that press and hold arbitrary positions of the link, and a link sending mechanism that sequentially transports the link chain at a constant speed.

[Embodiments of the invention] Embodiments of the present invention will be described below with reference to the drawings.

The link chain is obtained by first undergoing a process of quenching and tempering the entire chain at a predetermined temperature (first heat treatment), and then locally tempering and softening the chain (second heat treatment).

This second heat treatment step is the subject of the present invention, and this local softening device will be explained with reference to FIGS. 1 to 3.

The local softening device 20 has a guide rail 22 arranged linearly across both the front and rear ends of the stage 21, and a hook 2 at the end of the guide rail 22 that can be freely engaged with and detached from each link 5.
A link feeding mechanism 25 is provided at the front end of the guide rail 22 in sliding contact with the chain link 11. A rotatable endless wire brush 26 is provided so that scale adhering to the chain link 11 can be rubbed off.

Furthermore, one link 5 is installed at the center of the stage 21.
A pair of link positioning levers 2-7, which can be housed or released one by one, are disposed facing each other, and the link positioning levers 2-7 are arranged so that the links 5 set here are always horizontal.
A drive mechanism (not shown) is provided to control 7.

A link heating device 28 is disposed at the intermediate portion of the link positioning lever 27, so that each link 5 of the link chain 11 that is successively fed is locally heated here. .

The link heating device 28 includes a plurality of electrodes 29 that can hold the link 5 with a constant pressure from above and below, an air cylinder 30 that drives and controls the electrodes 29, and a commercial frequency current supplied to the electrodes 29. A pair of nozzles 31 are provided near the electrode 29, from which cooling water is supplied to the link 5.
This allows it to be sprayed towards the target.

Next, the action of the local softening device @20 mentioned above will be explained.

The link chain 11, which is hardened in a suitable heating furnace and then tempered in cooling water to form a tempered martensitic structure throughout the links, is aligned in a straight line by a guide rail 22 and a link feeding mechanism 25. Although it is continuously transferred, after the scale attached to the link chain 11 is rubbed off by the rotating wire brush 26, each link 5 is brought into a horizontal state one by one by the link positioning lever 27 of the heating device f28. Settings are retained.

The link 5 held in this way is connected to the electrode 29 from above and below.
After clamping with a predetermined pressing force, when electricity is applied between the upper and lower electrodes 29 via the link 5, Joule heat corresponding to the contact resistance between the link 5 and the two electrodes is concentrated in the local area clamped by the electrode 29. Then, quench this area.

Next, the heated portion of the link 5 is cooled and tempered by cooling water injected from the nozzle 31.

As a result, the links 5 are softened due to local differences in hardness, resulting in increased toughness and a link chain 11 with excellent elongation at break, load at break, and Charpy strength.

In addition, the above-mentioned quenching and tempering temperature allows the current value to be applied to the electrode 29 to the link 5 to be set accurately by appropriately adjusting the area, pressing force, and applied voltage of the electrode 29, and the energization time can also be set arbitrarily. , it is possible to achieve much higher precision than high-frequency induction heating.

Of course, since the Joule heat generated in the link 5 is concentrated in the area held between the electrodes 29, any local part (for example, the welded part of the link 5) can be accurately heat-treated.

[Effects of the Invention] As described above, according to the present invention, a region that requires local heat treatment is held under pressure between electrodes, and a predetermined frequency current is applied thereto.
Since the local softening treatment is performed by generating Joule heat in the clamping part, heat treatment can be performed at an accurate temperature only on the parts that really require heat treatment, such as the welded parts of the link, so it can be applied to any hardness. The device is configurable and has a simple configuration, so the equipment cost is low.

[Brief explanation of the drawing]

FIGS. 1 to 3 relate to embodiments of the present invention, and FIGS.
The figure is a plan view of a local softening device that locally heat-treats links, FIG. 2 is a front view of the same device, FIG. 3 is a front view of an electrode that is the main part of the same device, and FIG. 4 is a front view of an electrode to be subjected to heat treatment. FIG. 5 is an explanatory plan view showing the state of stress distribution due to the external shape of the link.

Claims (1)

[Claims] A guide rail that aligns the link chain in a straight line,
a link feeding mechanism that sequentially transports the link chain at a constant speed; a link positioning mechanism that holds and sets each link of the link chain in a predetermined state one by one; Link chain local softening device consisting of multiple electrodes held together.